package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.Arrays;

import org.apache.lucene.store.IndexInput;

/**
 * Implements the skip list reader for the default posting list format that
 * stores positions and payloads.
 * 
 */
class DefaultSkipListReader extends MultiLevelSkipListReader {
	private boolean currentFieldStoresPayloads;
	private long freqPointer[];
	private long proxPointer[];
	private int payloadLength[];

	private long lastFreqPointer;
	private long lastProxPointer;
	private int lastPayloadLength;

	DefaultSkipListReader(IndexInput skipStream, int maxSkipLevels,
			int skipInterval) {
		super(skipStream, maxSkipLevels, skipInterval);
		freqPointer = new long[maxSkipLevels];
		proxPointer = new long[maxSkipLevels];
		payloadLength = new int[maxSkipLevels];
	}

	void init(long skipPointer, long freqBasePointer, long proxBasePointer,
			int df, boolean storesPayloads) {
		super.init(skipPointer, df);
		this.currentFieldStoresPayloads = storesPayloads;
		lastFreqPointer = freqBasePointer;
		lastProxPointer = proxBasePointer;

		Arrays.fill(freqPointer, freqBasePointer);
		Arrays.fill(proxPointer, proxBasePointer);
		Arrays.fill(payloadLength, 0);
	}

	/**
	 * Returns the freq pointer of the doc to which the last call of
	 * {@link MultiLevelSkipListReader#skipTo(int)} has skipped.
	 */
	long getFreqPointer() {
		return lastFreqPointer;
	}

	/**
	 * Returns the prox pointer of the doc to which the last call of
	 * {@link MultiLevelSkipListReader#skipTo(int)} has skipped.
	 */
	long getProxPointer() {
		return lastProxPointer;
	}

	/**
	 * Returns the payload length of the payload stored just before the doc to
	 * which the last call of {@link MultiLevelSkipListReader#skipTo(int)} has
	 * skipped.
	 */
	int getPayloadLength() {
		return lastPayloadLength;
	}

	protected void seekChild(int level) throws IOException {
		super.seekChild(level);
		freqPointer[level] = lastFreqPointer;
		proxPointer[level] = lastProxPointer;
		payloadLength[level] = lastPayloadLength;
	}

	protected void setLastSkipData(int level) {
		super.setLastSkipData(level);
		lastFreqPointer = freqPointer[level];
		lastProxPointer = proxPointer[level];
		lastPayloadLength = payloadLength[level];
	}

	protected int readSkipData(int level, IndexInput skipStream)
			throws IOException {
		int delta;
		if (currentFieldStoresPayloads) {
			// the current field stores payloads.
			// if the doc delta is odd then we have
			// to read the current payload length
			// because it differs from the length of the
			// previous payload
			delta = skipStream.readVInt();
			if ((delta & 1) != 0) {
				payloadLength[level] = skipStream.readVInt();
			}
			delta >>>= 1;
		} else {
			delta = skipStream.readVInt();
		}
		freqPointer[level] += skipStream.readVInt();
		proxPointer[level] += skipStream.readVInt();

		return delta;
	}
}
